Analog Interface Sin/Cos (1Vpp) For Functional Safety; General Information; Processing The Safety Incremental G-Interface - Balluff BML Información Básica

Interfaces for BML Magnetic Encoder System
2
Interfaces (continued)
2.7 Analog interface sin/cos (1Vpp) for functional
safety
Position processing for the G-interface must be performed
as for the sin/cos interface (1Vpp).
2.7.1

General information

BML sensors with the G-interface may be used in safety
applications up to Safety Integrity Level 2 (SIL 2) per
EN 61800-5-2 / EN 62061 / IEC 61508 and Performance
Level d (PL d) per EN ISO 13849-1.
Sensors from series BML with G-interface provide the
safety function safe incremental value. Here safe
processing and transmission of the incremental rough
position information of the measuring system is
implemented via the analog sine/cosine interface. For
safety applications which use the function safe incremental
value only the rough position obtained from the quadrant
detection of A and B may be used.
Some sensors from series BML with G-interface also
provide the safety function safe absolute value. Here the
absolute position value is generated and transmitted
without safety. However a higher level plausibility check is
made between the safe relative rough position information
and a safe absolute value with the accuracy of the relative
rough position information (see Section 2.7.3 on
page 20). The other sensor interfaces (BiSS, SSI,
IO-Link, RS422, HTL...) may not be used alone in safety
applications!
For safe operation the sensor must be used in a safe
overall application. The user must consider the entire
safety chain of the safety function (e.g. use of a safety
controller) to determine the achieved SIL and PL.
Several Balluff BML sensors with G-interface are available
which are listed in the document BML-SIL-2 Sensors
(Doc No. 934186).
The document BML-SIL-2 Sensors
(Doc No. 934186) can be downloaded from the
Internet at www.balluff.com or requested by
email to service@balluff.de.
If the sensor is supplied with voltage that is
isolated from the processing electronics, the
GND for this voltage must be connected to the
GND of the processing electronics.
In addition to these instructions, refer also to the
instructions from the respective user's guide.
www.balluff.com
2.7.2

Processing the safety incremental G-interface

From the four signals +A (+sin), −A (−sin), +B (+cos),
−B (−cos) the differential signals A and B are formed as
follows:
A = +A (+sin) − (−A (−sin))
B = +B(+cos) − (−B (−cos))
For safety applications which use the function safe
incremental value only the rough position obtained from
the quadrant detection of A and B may be used. The
trigger levels for quadrature detection may be no higher
than ±100 mV.
The safety controller must perform the error detection by
determining and monitoring the pointer length (Z) of the
two differential signals using the following algorithm:
Z = (A² + B²)
The pointer length Z must be determined with a frequency
of at least 500 Hz. The pointer length Z must be monitored
for the limits Z = 0.25 V and Z
u
are exceeded or undershot, a safe state of the overall
system must be initiated within the process safety time.
An error occurring in the sensor can not be detected
sooner than after a movement of one period using pointer
length monitoring.
The evaluation circuit must be dimensioned such that the
pointer length at maximum travel speed (surface speed)
v and the corresponding period length p of the system
max
can be determined.
The maximum frequency of the A and B signals can be
determined as follows:
f = v / p
max max
The maximum frequency for quadrature determination is
calculated as follows:
f = 4 × v /p
max max
For safety processing only the quadrants of the
sin/cos-signals may be used. Interpolation of the
sin/cos signals is not permitted for the safe path.
Sin/cos signals (fine position) may however be used for
controlling drives outside of a safety function.
= 0.675 V. If these limits
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